Subsurface wells are typically constructed using steel casings which terminate within or through a reservoir zone of interest, such as where oil and gas is located. Using well-known perforation techniques or by the installation of slotted liners, recoverable resources are able to be produced at the surface through the casing or a secondary string of steel tubulars known as production tubing. It has generally not been of interest to produce fluid samples from above the region of interest.
The U.S. EPA has introduced a new classification of wells, referred to as Class VI injection wells specifically for injecting CO2 into the subsurface. As part of the criteria for installation of a Class VI well, it is required to directly confirm no contamination of the lowermost overlying underground source of drinking water. This would require a fluid sample be taken at this location above the CO2 storage reservoir.
Hydraulic fracturing technology used to recover oil and gas from tight shales can damage cement seals and form leakage pathways along casings. Being able to sample fluids behind casings would enable well operators to identify problematic cement seals and enable mitigation steps to be taken before migration of contaminants into overlying water formations.
PCT International Patent Application No. 2011/035953 discloses a tube-in-tube system comprising: (a) an outer conduit having a proximal end and a distal end, and (b) an inner conduit having a proximal end and a distal end, wherein the inner conduit is disposed within the outer conduit, wherein the proximal end of the inner conduit is in fluid communication with a first aperture, and the proximal end of the outer conduit is in fluid communication with a second aperture, and the distal ends of the inner and outer conduits are in fluid communication with each other and to a third aperture.
Other methods and/or devices have been disclosed by U.S. Pat. Nos. 4,369,654; 5,035,149; and, 5,692,565. Such methods and/or devices have among others, a disadvantage that a new perforation is required for each sample which must then be sealed. In addition, it is required that production through the wellbore be halted while sampling to lower a tool into the well.